Trench structures for three-dimensional memory devices

ABSTRACT

The present disclosure describes method and structure of a three-dimensional memory device. The memory device includes a substrate and a plurality of wordlines extending along a first direction over the substrate. The first direction is along the x direction. The plurality of wordlines form a staircase structure in a first region. A plurality of channels are formed in a second region and through the plurality of wordlines. The second region abuts the first region at a region boundary. The memory device also includes an insulating slit formed in the first and second regions and along the first direction. A first width of the insulating slit in the first region measured in a second direction is greater than a second width of the insulating slit in the second region measured in the second direction.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the priority of Chinese Patent Application No.201710131738.5 filed on Mar. 7, 2017 and PCT Patent Application No.PCT/CN2018/077706 filed on Mar. 1, 2018, the entire contents of whichare incorporated herein by reference.

BACKGROUND

Flash memory devices have undergone rapid development. Flash memorydevices can store data for a considerably long time without powering,and have the advantages such as high integration level, fast access,easy erasing and rewriting. Flash memory devices have thus been widelyused in different fields such as automation and control. To furtherimprove the bit density and reduce cost, three-dimensional NAND flashmemory devices have been developed.

A three-dimensional NAND flash memory device often includes a stack ofgate electrodes arranged over a substrate, with a plurality ofsemiconductor channels through and intersecting the wordlines, into thesubstrate. The bottom gate electrodes function as bottom select gates.The top gate electrodes function as top select gates. The wordlines/gate electrodes between the top select gate electrodes and thebottom gate electrodes function as wordlines. The intersection of awordline and a semiconductor channel forms a memory cell. The top selectgates are connected to wordlines for row selection, and the bottomselect gates are connected to bitlines for column selection.

BRIEF SUMMARY

Embodiments of 3D memory architectures and fabrication methods thereofare disclosed herein.

In some embodiments, a slit structure layout includes a slit openingwhich includes a wordline staircase slit opening and an array slitopening. The slit structure layout also includes channel openingslocated between adjacent slit openings. The wordline staircase slitopening abuts the array slit opening. The length of the slit openingsextend along a lateral direction and the widths of the slit openings aremeasured perpendicular to the lateral direction. A width of the wordlinestaircase slit opening is greater than a width of the array slitopening.

In some embodiments, the width of the wordline staircase slit opening isgreater than the width of the array slit opening by about 10 nm to about50 nm (inclusive). The width of the wordline staircase slit opening canbe uniform.

In some embodiments, the end structure of the wordline staircase slitopening that is further away from the array slit includes a curved endstructure. The curved end structure can include an arc-shaped structurewith the arc facing the array slit opening.

In some embodiments, the width of the wordline staircase slit openingincreases towards the end structure that is further away from the arrayslit opening.

In some embodiments, a slit structure layout also includes contactstructures formed adjacent to the wordline staircase slit opening, andrespective portions of a contact structure and the end structure of thewordline staircase slit opening that are furthest away from the arrayslit opening are separated by about 0.5 μm to about 2 μm, inclusive.

In some embodiments, a semiconductor device can include any one of theslit structure layout design described above, and the semiconductordevice can include a substrate, a slit structure formed in thesubstrate. The slit structure includes wordline staircase slits andarray slits. Channels can be located between adjacent slits. Thewordline staircase slits abut the array slits. Width of the wordlinestaircase slit opening is greater than a width of the array slitopening, and the widths are measured along a direction that isperpendicular to the direction in which the slits extend along. In someembodiments, the semiconductor device is a three-dimensional memorydevice.

In some embodiments, the present disclosure provides a method for makinga semiconductor device, the method includes providing a substrate havinga wordline staircase region and an array region. Forming a mask patternon the substrate, the mask pattern corresponds to the slit structurelayout described above. Etching the substrate according to the maskpattern and form wordline staircase slit and array slit.

According to the above disclosure, the present disclosure describes aslit structure layout, semiconductor structures, and methods of makingsemiconductor structures. The width of a wordline staircase slit isgreater than the width of an array slit. The widths of the slit openingsare measured along a direction that is perpendicular to the direction ofthe slit length. Due to the increased width of the wordline staircaseslit opening, a bottom width of the wordline staircase slit opening isalso increased. Metal material disposed in the wordline staircase slitswith increased widths can result in more uniform metal dispose and avoidmetal material agglomeration, which in turn provides at least thebenefits of effectively separating wordline structures from differenttiers and avoid shorts or leakage current between wordline structures.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated herein and form a partof the specification, illustrate embodiments of the present disclosureand, together with the description, further serve to explain theprinciples of the present disclosure and to enable a person skilled inthe pertinent art to make and use the present disclosure.

FIG. 1 illustrates an exemplary three-dimensional memory device.

FIGS. 2A and 2B illustrate respectively a top and a cross-section of athree-dimensional memory structure, according to some embodiments.

FIGS. 3A and 3B illustrate respectively a top and cross-section of athree-dimensional memory structure, according to some embodiments.

FIG. 4A illustrate a top of a three-dimensional memory structure,according to some embodiments.

FIGS. 4B-4D illustrate cross-sections of a three-dimensional memorystructure, according to some embodiments.

FIGS. 5A and 5B illustrate cross-sections of a three-dimensional memorystructure, according to some embodiments.

FIGS. 6-8 illustrate tops of a three-dimensional memory structure,according to some embodiments.

FIG. 9 illustrates an exemplary fabrication process for forming athree-dimensional memory structure, according to some embodiments.

DETAILED DESCRIPTION

Although specific configurations and arrangements are discussed, itshould be understood that this is done for illustrative purposes only. Aperson skilled in the pertinent art will recognize that otherconfigurations and arrangements can be used without departing from thespirit and scope of the present disclosure. It will be apparent to aperson skilled in the pertinent art that the present disclosure can alsobe employed in a variety of other applications.

It is noted that references in the specification to “one embodiment,”“an embodiment,” “an example embodiment,” “some embodiments,” etc.,indicate that the embodiment described may include a particular feature,structure, or characteristic, but every embodiment may not necessarilyinclude the particular feature, structure, or characteristic. Moreover,such phrases do not necessarily refer to the same embodiment. Further,when a particular feature, structure or characteristic is described inconnection with an embodiment, it would be within the knowledge of aperson skilled in the pertinent art to effect such feature, structure orcharacteristic in connection with other embodiments whether or notexplicitly described.

In general, terminology may be understood at least in part from usage incontext. For example, the term “one or more” as used herein, dependingat least in part upon context, may be used to describe any feature,structure, or characteristic in a singular sense or may be used todescribe combinations of features, structures or characteristics in aplural sense. Similarly, terms, such as “a,” “an,” or “the,” again, maybe understood to convey a singular usage or to convey a plural usage,depending at least in part upon context.

It should be readily understood that the meaning of “on,” “above,” and“over” in the present disclosure should be interpreted in the broadestmanner such that “on” not only means “directly on” something but alsoincludes the meaning of “on” something with an intermediate feature or alayer therebetween, and that “above” or “over” not only means themeaning of “above” or “over” something but can also include the meaningit is “above” or “over” something with no intermediate feature or layertherebetween (i.e., directly on something).

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper,” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

As used herein, the term “substrate” refers to a material onto whichsubsequent material layers are added. The substrate itself can bepatterned. Materials added on top of the substrate can be patterned orcan remain unpatterned. Furthermore, the substrate can include a widearray of semiconductor materials, such as silicon, germanium, galliumarsenide, indium phosphide, etc. Alternatively, the substrate can bemade from an electrically non-conductive material, such as a glass, aplastic, or a sapphire wafer.

As used herein, the term “layer” refers to a material portion includinga region with a thickness. A layer can extend over the entirety of anunderlying or overlying structure, or may have an extent less than theextent of an underlying or overlying structure. Further, a layer can bea region of a homogeneous or inhomogeneous continuous structure that hasa thickness less than the thickness of the continuous structure. Forexample, a layer can be located between any pair of horizontal planesbetween, or at, a top surface and a bottom surface of the continuousstructure. A layer can extend horizontally, vertically, and/or along atapered surface. A substrate can be a layer, can include one or morelayers therein, and/or can have one or more layer thereupon, thereabove,and/or therebelow. A layer can include multiple layers. For example, aninterconnect layer can include one or more conductor and contact layers(in which contacts, interconnect lines, and/or vias are formed) and oneor more dielectric layers.

As used herein, the term “nominal/nominally” refers to a desired, ortarget, value of a characteristic or parameter for a component or aprocess operation, set during the design phase of a product or aprocess, together with a range of values above and/or below the desiredvalue. The range of values can be due to slight variations inmanufacturing processes or tolerances. As used herein, the term “about”indicates the value of a given quantity that can vary based on aparticular technology node associated with the subject semiconductordevice. Based on the particular technology node, the term “about” canindicate a value of a given quantity that varies within, for example,10-30% of the value (e.g., ±10%, ±20%, or ±30% of the value).

As used herein, the term “three-dimensional memory device” refers to asemiconductor device with vertically oriented strings of memory celltransistors (referred to herein as “memory strings,” such as NANDstrings) on a laterally-oriented substrate so that the memory stringsextend in the vertical direction with respect to the substrate. As usedherein, the term “vertical/vertically” means nominally perpendicular tothe lateral surface of a substrate.

Trends in three-dimensional NAND memory industry include the reductionof device dimensions and the simplification of fabrication process. In athree-dimensional NAND memory device, memory cells for storing data areembedded in a stack of wordlines (control gate electrodes) and thesemiconductor channels formed through the stack. Each wordline isseparately connected to a metal contact via, which is further connectedto a metal interconnect and an external circuit (e.g., control circuit).This permits writing and erasing data in the memory cells to becontrolled from an external circuit. Thus, the number of metal contactvias is often equal to the number of wordlines. As the demand of storagecapacity increases, numerous memory cells, which are formed by anincreased number of wordlines and semiconductor channels, can be formedin a NAND memory device.

Adjacent stacks of wordlines or control gate electrodes are separated bygate line slits, which are deep trenches formed vertically through thestacks and filled with insulating material. The gate line slits canextend through an array region as well as a wordline staircase region.Accordingly, as the need for more wordlines increases, the stack heightof the wordline layers can be increased, which leads to gate line slitswith higher aspect ratios (trench height divided by trench width).Trenches with a high aspect ratio can be challenging for devicefabrication processes due to the difficulty of uniform dispose and/oretching within the trenches. For example, an array region and a wordlinestaircase region are typically formed of different materials. As gateline slit extends through both regions, the etching profile can vary dueto different etching performance on different materials. The variationin etching profile can be exacerbated by increased trench aspect ratio,which can cause additional metal remaining at the bottom of the trenchafter gate electrodes are separated by etching back the disposed metal.And current leakage or shorts between adjacent gate electrodes caused bythe remaining metal can lead to device failure.

The present disclosure describes a three-dimensional NAND memory devicein which the width of gate line slit is increased in the wordlinestaircase regions in comparison to its width in the array region. Thedisclosed method and structure can be incorporated intothree-dimensional NAND memory device design and manufacture withoutadding any additional fabrication steps or additional masks. Increasingthe gate line slit width at the top surface of the wordline staircaseregion can lead to an increased width at the bottom of the gate lineslit. A benefit, among others, of increasing the gate line slit width inthe wordline staircase region facilitates uniform metal dispose andavoids metal agglomeration at the bottom of the gate line slit. Uniformmetal dispose within the gate line slit in turn provides uniform gateelectrode material etch back and prevents current leakage or shortsbetween adjacent gate electrodes.

In the present disclosure, for ease of description, “tier” is used torefer to elements of substantially the same height along the verticaldirection. For example, a wordline and the underlying gate dielectriclayer can be referred to as “a tier,” a sacrificial layer and theunderlying insulating layer can together be referred to as “a tier,” awordline and the underlying insulating layer can together be referred toas “a tier,” wordlines of substantially the same height can be referredto as “a tier of wordlines” or similar, and so on.

FIG. 1 illustrates a block 100 of a three-dimensional NAND flash memorydevice. The flash memory device includes a substrate 101, an insulatinglayer 103 over substrate 101, a tier of bottom select gate electrodes104 over insulating layer 103, and a plurality of tiers of control gateelectrodes 107 (e.g., 107-1, 107-2, and 107-3) stacking on top of bottomselect gate electrodes 104. Flash memory device 100 also includes a tierof top select gate electrodes 109 over the stack of control gateelectrodes 107, doped source line regions 120 in portions of substrate101 between adjacent bottom select gate electrodes 104, andsemiconductor channels 114 through top select gate electrodes 109,control gate electrodes 107, bottom select gate electrodes 104, andinsulating layer 103. Semiconductor channel 114 (illustrated by a dashedeclipse) includes a memory film 113 over the inner surface ofsemiconductor channel 114 and a core filling film 115 surrounded bymemory film 113 in semiconductor channel 114. The flash memory device100 further includes a plurality of bitlines 111 disposed on andconnected to semiconductor channels 114 over top select gate electrodes109. A plurality of metal interconnects 119 are connected to the gateelectrodes (e.g., 104, 107, and 109) through a plurality of metalcontacts 117. Insulating layers between adjacent tiers of gateelectrodes are not shown in FIG. 1, but would be apparent to a person ofordinary skill in the memory art. The gate electrodes are also referredto as the wordlines, which include top select gate electrodes 109,control gate electrodes 107, and bottom select gate electrodes 104.

In FIG. 1, for illustrative purposes, three tiers of control gateelectrodes 107-1, 107-2, and 107-3 are shown together with one tier oftop select gate electrodes 109 and one tier of bottom select gateelectrodes 104. Each tier of gate electrodes have substantially the sameheight over substrate 101. The gate electrodes of each tier areseparated by gate line slits 108-1 and 108-2 through the stack of gateelectrodes. Each of the gate electrodes in a same tier is conductivelyconnected to a metal interconnect 119 through a metal contact via 117.That is, the number of metal contacts formed on the gate electrodesequals the number of gate electrodes (i.e., the sum of all top selectgate electrodes 109, control gate electrodes 107, and bottom select gateelectrodes 104). Further, the same number of metal interconnects isformed to connect to each metal contact via 117.

For illustrative purposes, similar or same parts in a three-dimensionalNAND device are labeled using same element numbers. However, elementnumbers are merely used to distinguish relevant parts in the DetailedDescription and do not indicate any similarity or difference infunctionalities, compositions, or locations. The structures 200-800illustrated in FIG. 2A to FIG. 8 are each portions of athree-dimensional NAND memory device. Other parts of the memory deviceare not shown for ease of description. Although using athree-dimensional NAND device as an example, in various applications anddesigns, the disclosed structure can also be applied in similar ordifferent semiconductor devices to, e.g., reduce the leakage currentbetween adjacent wordlines. The specific application of the disclosedstructure should not be limited by the embodiments of the presentdisclosure. For illustrative purposes, wordlines and gate electrodes areused interchangeably to describe the present disclosure. In variousembodiments, the number of layers, the methods to form these layers, andthe specific order to form these layers may vary according to differentdesigns and should not be limited by the embodiments of the presentdisclosure. It should be noted that the “x” and “y” directionsillustrated in these figures are for clarity purposes and should not belimiting. Exemplary structures shown in FIGS. 2A-8 can be portions ofthree-dimensional memory devices, and the three-dimensional memorydevice can include wordline staircase regions extending in any suitabledirection such as, for example, positive y direction, negative ydirection, positive x direction, negative x direction, and/or anysuitable directions.

FIGS. 2A and 2B illustrate an exemplary substrate 200 for forming athree-dimensional memory structure, according to some embodiments. FIG.2A is a top view 201 of structure 200, and FIG. 2B is a cross-sectionalview 202 of structure 200 along 2-2′ direction. In some embodiments,substrate 200 includes a base substrate 210 and a material layer 240over substrate 210. Base substrate 210 can provide a platform forforming subsequent structures. Material layer 240 can include analternating stack (e.g., dielectric layer pairs/stack) having a firstmaterial/element 211 and a second material/element 212 arrangedalternatingly. Material layer 240 can be used to form subsequentwordlines over base substrate 210. For illustrative purposes, fourtiers/pairs of first material 211/second material 212 are shown todescribe the present disclosure. In various applications and designs,material layer 240 can include any suitable number of tiers/pairs offirst material/second material stacking together, depending on thedesign of the three-dimensional memory device. For example, materiallayer 240 can include 64 tiers/pairs of first material/second materialstacking together, which subsequently forms 64 tiers of wordline in thethree-dimensional memory device.

In some embodiments, base substrate 210 includes any suitable materialfor forming the three-dimensional memory structure. For example, basesubstrate 210 can include silicon, silicon germanium, silicon carbide,silicon on insulator (SOI), germanium on insulator (GOI), glass, galliumnitride, gallium arsenide, and/or other suitable III-V compound.

In some embodiments, material layer 240 includes an alternating stack ofinsulating layers 211 (i.e., first element or first material) andsacrificial layers 212 (i.e., second element or second material),arranged vertically (along z-axis) over base substrate 210. Forillustrative purposes, the insulating layer 211 and the correspondingunderlying sacrificial layer 212 are referred to as an element pair ormaterial pair of the same tier. In some embodiments, sacrificial layers212 are removed subsequently for disposing gate metal material forforming wordlines. In some embodiments, sacrificial layers 212 includeany suitable material different from insulating layers 211. For example,sacrificial layers 212 can include poly-crystalline silicon, siliconnitride, poly-crystalline germanium, and/or poly-crystallinegermanium-silicon. In some embodiments, sacrificial layers 212 includesilicon nitride. Insulating layers 211 can include any suitableinsulating materials, e.g., silicon oxide. Material layer 240 can beformed by alternatingly disposing insulating layers 211 and sacrificiallayers 212 over base substrate 210. For example, an insulating layer 211can be disposed over base substrate 210, and a sacrificial layer 212 canbe disposed on insulating layer 211, and so on and so forth. The disposeof insulating layers 211 and sacrificial layers 212 can be include anysuitable methods such as chemical vapor deposition (CVD), physical vapordeposition (PVD), plasma-enhanced CVD (PECVD), sputtering, metal-organicchemical vapor deposition (MOCVD), and/or atomic layer deposition (ALD).In some embodiments, insulating layers 211 and sacrificial layers 212are each formed by CVD. For illustrative purposes, substrate 200 isdivided into two regions, i.e., regions A and B. In the subsequentfabrication of the three-dimensional memory structure, wordlines (gateelectrodes) are formed through regions A and B along a horizontaldirection (e.g., x-axis) substantially parallel to the top surface ofsubstrate 200. After the subsequent fabrication steps discussed below,wordline staircase structures are substantially formed in region A, andsemiconductor channels are formed substantially in region B. It shouldbe noted that, regions A and B are for ease of description only, and arenot intended to indicate physical division of substrate 200 ordimensions of substrate 200.

FIGS. 3A and 3B illustrate an exemplary structure 300 for forming thethree-dimensional memory device, according to some embodiments. FIG. 3Ais a top view 301 of structure 300, and FIG. 3B is a cross-sectionalview 302 of structure 300 along 3-3′ direction. The structureillustrated by FIGS. 3A and 3B can be referred to as a “staircasestructure” or a “stepped cavity structure.” Terms “staircase structure,”“stepped cavity structure,” or similar refer to a structure havingstepped surfaces. In the present disclosure, “stepped surfaces” refer toa set of surfaces that include at least two horizontal surfaces (e.g.,along x-y plane) and at least two (e.g., first and second) verticalsurfaces (e.g., along z-axis) such that each of a first horizontalsurface and a second horizontal surface is adjoined to a first verticalsurface that extends upward from a first edge of the first horizontalsurface, and the second horizontal surface is also adjoined to a secondvertical surface that extends downward from a second edge of the secondhorizontal surface. A “step” or “staircase” refer to a vertical shift inthe height of a set of adjoined surfaces.

The staircase structure can have various stepped surfaces, referring toFIGS. 3A and 3B, such that the horizontal cross-sectional shape of thestaircase structure changes in step as a function of the verticaldistance from the top surface of structure 300 (i.e., top surface ofstructure 300). In some embodiments, structure 300 is formed fromstructure 200 by repetitively etching insulating layers 211 andsacrificial layers 212 of material layer 240, e.g., along verticaldirection (i.e., z-axis), using a mask. For illustrative purposes, thestructure formed by etching material layer 240 is referred to as stack240′ over base substrate 210. Accordingly, as shown in FIGS. 3A and 3B,structure 300 can have a plurality of insulating layers (e.g., 211-1 to211-4) and a plurality of sacrificial layers (e.g., 212-1 to 212-3).Except for the bottom insulating layer 211-4, each insulating layer 211can form a pair or a tier with an adjacent and underlying sacrificiallayer with substantially same length/shape along y axis. For example,insulating layer 211-1 and sacrificial layer 212-1 form a first tier,and insulating layer 211-2 and sacrificial layer 212-2 form a secondtier, so on and so forth. The etching of the insulating layer and thesacrificial layer in each pair can be performed in one etching processor different etching processes. The etching processes can be plasmaprocesses such as, for example, a reactive ion etching (ME) processusing oxygen-based plasma. In some embodiments, the RIE etching processmay include etchant gas such as, for example, carbon tetrafluoride(CF₄), sulfur hexafluoride (SF₆), fluoroform (CHF₃), and/or othersuitable gases. Numerous other etching methods can also be suitable.After the formation of the stepped surfaces, the mask can be removed,e.g., by ashing, or by using a photoresist stripper. In someembodiments, multiple photoresist layers and/or multiple etchingprocesses are employed to form the stepped surfaces. As shown in FIG.3A, in structure 300, the insulating layer (i.e., 211-1 to 211-4) ofeach tier is exposed along z axis.

FIGS. 4A-4D illustrate an exemplary structure 400 for forming thethree-dimensional memory device, according to some embodiments. FIG. 4Ais a top view 401 of structure 400, and FIG. 4B is a cross-sectionalview 402 of structure 400 along the 4 a-4 a′ direction. FIG. 4C is across-sectional view 403 of structure 400 along the 4 b-4 b′ direction.FIG. 4D is a cross-sectional view 404 of structure 400 along the 4 c-4c′ direction. In some embodiments, structure 400 includes a plurality ofsemiconductor channels 220 formed in region B. Semiconductor channels220 can be distributed as arrays along y-axis, and each array isseparated by a suitable distance of which can be any reasonable distanceaccording to the design/layout of the three-dimensional memory device.Each array of semiconductor channels 220 can have the same number ordifferent numbers of semiconductor channels 220. For illustrativepurposes, referring to FIG. 4A, in the present disclosure, each arrayincludes 5 semiconductor channels 220, forming a 3 by 2 arrayarrangement. Semiconductor channels 220 can be formed through stack 240substantially along z-axis and into base substrate 210 for thesubsequent formation of source and/or drain of the three-dimensionalmemory device. Semiconductor channels 220 and subsequently formedwordlines can form memory cells, e.g., for storing data, of thethree-dimensional memory device.

Each semiconductor channel 220 can substantially have a shape of apillar along the z-axis and can include a plurality of layerssurrounding one another (not shown in the figures of the presentdisclosure). For example, semiconductor channel 220 can include adielectric core positioned along z-axis and substantially in the centerof semiconductor channel 220. The dielectric core can be surrounded by asemiconductor channel film. The semiconductor channel film can besurrounded by a memory film. The dielectric core, the semiconductorchannel film, and the memory film can each include one or more layers,and can together fill in a channel hole to form semiconductor channel220. In some embodiments, the channel holes can be formed by patterningstack 240′ using a mask and etching the portions of stack 240 exposed bythe patterned mask using a suitable etching process, e.g., dry etchand/or wet etch. The channel holes can be through stack 240 andsubstantially into base substrate 210. The mask can be removed after thechannel holes are formed.

For example, the memory film can be formed over and contacting thesidewall of a channel hole. In some embodiments, the memory film caninclude one or more block dielectric layers over the sidewall of thechannel hole to insulate other layers in the channel hole from stack240′ surrounding the channel hole. The memory film can also include astorage unit layer (memory layer) over and surrounded by the blockdielectric layers for trapping charges and forming a plurality of chargestorage regions along z-axis. The memory film can also include atunneling layer (e.g., tunneling dielectric) over and surrounded by thememory layer. Charge tunneling can be performed through the tunnelinglayer under a suitable electric bias. In some embodiments, chargetunneling can be performed through hot-carrier injection or byFowler-Nordheim tunneling induced charge transfer, depending on theoperation of the three-dimensional memory device.

The one or more block dielectric layers can include a first block layerwhich includes a dielectric metal oxide layer with a relatively highdielectric constant. Term “metal oxide” can include a metallic elementand non-metallic elements such as oxygen, nitrogen, and other suitableelements. For example, the dielectric metal oxide layer can includealuminum oxide, hafnium oxide, lanthanum oxide, yttrium oxide, tantalumoxide, silicates, nitrogen-doped compounds, alloys, etc. the first blocklayer can be disposed, for example, by CVD, ALD, pulsed laser deposition(PLD), liquid source misted chemical deposition, and/or other suitabledispose methods.

The one or more block dielectric layers can also include a second blocklayer which includes another dielectric layer over the dielectric metaloxide. The other dielectric layer can be different from the dielectricmetal oxide layer. The other dielectric layer can include silicon oxide,a dielectric metal oxide having a different composition than the firstblock layer, silicon oxynitride, silicon nitride, and/or other suitabledielectric materials. The second block layer can be disposed, forexample, by low pressure chemical vapor deposition (LPCVD), ALD, CVD,and/or other suitable dispose methods. In some embodiments, the one ormore block dielectric layers include silicon oxide, which is formed byCVD.

The storage unit layer can be sequentially formed over the one or moreblock dielectric layers. The storage unit layer can include a chargetrapping material, e.g., a dielectric charge trapping material (e.g.,silicon nitride) and/or a conductive material (e.g., doped polysilicon).In some embodiments, the dielectric charge trapping material includessilicon nitride and can be formed by CVD, ALD, PVD, and/or othersuitable methods.

The tunneling layer can be sequentially formed over the memory layer.The tunneling layer can include silicon oxide, silicon nitride, siliconoxynitride, dielectric metal oxides, dielectric metal oxynitride,dielectric metal silicates, alloys, and/or other suitable materials. Thetunneling layer can be formed by CVD, ALD, PVD, and/or other suitablemethods. In some embodiments, the tunneling layer includes siliconoxide, which is formed by CVD.

The semiconductor channel film can be sequentially formed over thetunneling layer. The semiconductor channel film can include one or morelayers of any suitable semiconductor materials such as silicon, silicongermanium, germanium, III-V compound material, II-VI compound material,organic semiconductor material, and/or other suitable semiconductormaterials. The semiconductor channel film can be formed by a suitablemethod such as metal-organic chemical vapor deposition (MOCVD), LPCVD,CVD, and/or other suitable methods. In some embodiments, thesemiconductor channel film is formed by depositing a layer of amorphoussilicon using CVD, followed by an annealing process such that theamorphous silicon is converted to single-crystalline silicon. In someembodiments, other amorphous material can be annealed to be crystallizedto form the semiconductor channel film.

The dielectric core can be formed over the semiconductor channel filmand to fill in the space at the center of the channel hole. Thedielectric core can include a suitable dielectric material such assilicon oxide and/or organosilicate glass. The dielectric core can beformed by a suitable conformal method (e.g., LPCVD) and/orself-planarizing method (e.g., spin coating). In some embodiments, thedielectric core includes silicon oxide and is formed by LPCVD.

Insulating material 413 can be formed semiconductor structure 400. Forexample, insulating material 413 can be formed on region A and the topsurface of insulating material 413 can be coplanar with the top surfaceof insulating layer 211-1. In some embodiments, insulating material 413is also formed on insulating layer 211-1, and channels 220 alsopenetrate insulating material 413. Insulating material 413 can includeany suitable insulating materials, e.g., silicon oxide. The dispose ofinsulating material 413 can be include any suitable methods such as CVD,PVD, PECVD, sputtering, MOCVD, and/or ALD. In some embodiments,insulating material 413 is formed by CVD. A planarization method suchas, for example, chemical mechanical polishing (CMP) can be used toplanarize the top surface of insulating material 413.

Structure 400 further includes a plurality of insulating trenches orvertical trenches, each formed between two arrays of semiconductorchannels 220 substantially along x-axis, to divide stack 240′ into aplurality of fingers, each finger extending substantially along x-axis.In the present disclosure, term “vertical” refers to “along z-axis,”“substantially perpendicular to x-y plane,” or similar. Wordlines can besubsequently formed in each finger. A vertical trench can include one ormore openings along x-axis. In some embodiments, the vertical trenchescan be used to replace sacrificial layers 211 with metal gate electrodematerial. For example, after gate electrode material is disposed betweenadjacent sacrificial layers 212 to forms wordline structures, an etchback process can be used to remove excessive metal gate electrodematerial from within the trench such that wordlines from different tierscan be electrically insulated. The trenches can be subsequently filledwith a suitable insulating material to form gate line slits, alsoreferred to as insulating spacers or insulating slits. That is,subsequently-formed wordlines in adjacent fingers can be insulated atthe locations filled with the insulating material.

For illustrative purposes, two adjacent vertical trenches 221 and 222are shown in FIGS. 4A-4D of the present disclosure. Vertical trench 221includes vertical trench 221A and 221B, respectively formed in regions Aand B. Similarly, vertical trench 222 includes vertical trench 222A and222B, respectively formed in regions A and B. The two adjacent verticaltrenches 221 and 222 divide structure 400 into Fingers 1, 2, and 3, eachincluding an array of semiconductor channels 220. Vertical trenches 221Aand 222A are used to divide subsequently-formed wordlines in differentfingers, while 221B and 222B of the vertical trenches are formed inregion B to divide arrays of semiconductor channels 220 in differentfingers along x-axis. The arrays of semiconductor channels 220 canrespectively form memory cells with subsequently-formed wordlines inFingers 1, 2, and 3.

Vertical trenches (e.g., 221 and 222) can be formed by forming a masklayer over stack 240′ and patterning the mask using, e.g.,photolithography, to form openings corresponding to the verticaltrenches in the patterned mask layer. A suitable etching process, e.g.,dry etch and/or wet etch, can be performed to remove portions of stack240′ exposed by the openings until the vertical trenches expose basesubstrate 210. The etching processes can be plasma processes such as,for example, an RIE process using oxygen-based plasma. In someembodiments, the RIE etching process may include etchant gas such as,for example, CF₄, SF₆, CHF₃, and/or other suitable gases. Numerous otheretching methods can also be suitable. The mask layer can be removedafter the formation of vertical trenches. In some embodiments, verticaltrenches are through each of the tiers in stack 240′ and divide stack240′ into a plurality of fingers along x-axis. A vertical trench caninclude one or more openings as described above along x-axis so thatsacrificial layer/insulating layer of adjacent fingers in each tier canbe connected through opening(s) of the vertical trench in between.

FIGS. 4C and 4D are respective cross-sectional view from lines 4 b-4 b′and 4 c-4 c′, which represents cross-sectional views of regions B and Arespectively. As shown in FIG. 4C, vertical trenches 221B and 222B areformed in region B where the semiconductor channels are formed, andtherefore are formed through alternating dielectric stacks of insulatinglayers 211-1 through 211-4 and sacrificial layers 212-1 through 212-3.The etching process described above can continue until the trenchreaches substrate 210. Due to material composition differences betweenregions A and B, the etching processes produce different etchingprofiles in these regions. For example, trenches 221A and 222A in regionA are substantially formed through insulating materials and one or morestaircase structures, while trenches 221B and 222B are formed throughthe stack of alternating dielectric materials. As described above, insome embodiments, the insulating layer 211 and insulating layer 413 caninclude silicon oxide. In some embodiments, sacrificial layer 212includes silicon nitride. The etching processes can be wet etchingprocesses that can lead to a more anisotropic etching profileperformance on silicon nitride material. The etchant for silicon nitridewet etching process can react with silicon nitride material and producea layer of polymer material on the sidewall during etching that protectsthe sidewalls from lateral etching. In contrast, less polymer materialis formed during silicon oxide wet etching process and more lateraletching can be observed, which results in a less anisotropic etchingprofile on silicon oxide material. As a result, trenches in region Aforms etching profiles that contain a tilted sidewall, which causestrench width at the top of the trench to be greater than trench width atthe bottom of the trench. In contrast, etch profiles in region B showsubstantially vertical sidewalls, which indicates trench width at thetop substantially equals the trench width at the bottom.

FIGS. 5A and 5B illustrate structure 500 for forming thethree-dimensional memory device, according to some embodiments. FIGS. 5Aand 5B illustrates the structures shown in FIGS. 4A and 4B aftersacrificial material is replaced by metal gate electrode material and anetch back process has been performed to isolate each layer of gateelectrode material and form wordlines 532-1 through 532-3. In someembodiments, the sacrificial layers can be removed by any suitableetching processes such as, for example, a dry etching process, a wetetching process, any other suitable etching processes, and/orcombinations thereof. After the sacrificial layers are removed,horizontal trenches are formed between insulating layers and gateelectrode material is disposed in the place of the sacrificial layersand in the horizontal trenches. For example, each tier of structure 500includes a gate metal material layer over the respective insulatinglayer 211. In some embodiments, structure 500 can be formed fromstructure 400 illustrated in FIGS. 4A-4D by filling replacingsacrificial layers 212 with a suitable gate electrode metal material.The gate electrode metal material can fill each horizontal trench alongx-y plane and cover the respective insulating layer 211. Gate metalmaterial layers can provide the base material for thesubsequently-formed wordlines (i.e., gate electrodes) 532-1 through532-3 after the etch back process. In some embodiments, gate electrodematerial can be formed by filling vertical trenches and the horizontaltrenches with a suitable conductive material. For example, a suitabledispose method, such as ALD can be used. In some embodiments, CVD, PVD,PECVD, other suitable methods, and/or combinations thereof, can beutilized to deposit the gate electrode material.

After the gate electrode material is disposed in the vertical andhorizontal trenches, an etch back process can be performed to removeexcessive gate electrode material from the vertical trenches such thatwordlines from different tiers can be electrically insulated. Etchprofiles of the vertical trenches in region B show substantiallyvertical sidewalls which can facilitate uniform metal dispose and inturn provides uniform etch back of gate electrode material throughoutthe height of the trench. For example, as shown in FIG. 5A, each layerof the formed wordline 532-1 through 532-3 formed after the etch backprocess is electrically insulated from one another because excessivegate electrode material is removed from the sidewalls of verticaltrenches 221B and 222B. In contrast, trenches in region A forms etchingprofiles that contain a tilted sidewall, which causes trench width atthe top of the trench to be greater than trench width at the bottom ofthe trench. The tapered profile causes non-uniform dispose of gateelectrode material into trenches 221A and 222A. For example, gateelectrode material tend to agglomerate at the bottom of trenches 221Aand 222A, and the etch back process may not completely remove excessivegate electrode material from the trench sidewalls at the bottom of thetrenches. The remaining gate electrode material (illustrated by dashedcircles 540) on the trench sidewalls can cause shorts or current leakagebetween tiers of wordline structures. For example, as shown in FIG. 5B,wordline 532-2 is electrically connected to wordline 532-3 due to theexcessive gate electrode material remaining on the sidewall after theetch back process.

Further structures are formed on exemplary structures to complete thethree-dimensional NAND memory devices and for the ease of descriptionthe details of formation of the other structures are omitted in thepresent disclosure. For example, metal contact vias can be formed overeach tier to connect wordlines of each tier to an external circuit. Insome embodiments, the metal contact vias are formed by patterning thedielectric stack to form a number of contact openings exposing thecontact areas on each tier, and filling the contact openings with asuitable conductive material to form the metal contact vias. Thepatterning process can include forming a mask over the dielectric stack,performing a photolithography process to define the contact openings inthe mask, and removing the material in the contact openings untildesired contact areas of wordline staircase region are exposed. Thecontact areas of each tier can be on one or more wordlines. Further, thecontact openings can be filled with a suitable conductive material,e.g., tungsten, aluminum, and/or copper.

FIGS. 6-8 illustrate top views of three-dimensional NAND memory devicesin which the width of gate line slit is increased in the wordlinestaircase regions in comparison to its width in the array region.Increasing the gate line slit width at the top surface of the wordlinestaircase region can lead to an increased width at the bottom of thegate line slit. A benefit, among others, of increasing the gate lineslit width in the wordline staircase region is facilitating uniformmetal dispose and avoiding metal agglomeration at the bottom of the gateline slit. Uniform metal dispose within the gate line slit in turnprovides uniform gate electrode material etch back and prevents currentleakage or shorts between adjacent gate electrodes. In various designsand applications, design and location of gate line slits can varyaccording to different design rules and should not be limited by theembodiments of the present disclosure.

FIG. 6 illustrates exemplary structure 600 for forming thethree-dimensional memory device, according to some embodiments. FIG. 6is a top view 601 of exemplary structure 600 which includes wordlinestaircase region A and array region B. Regions A and B abut each otherat a region boundary 602, marked by the dotted line. An array ofsemiconductor channels 620 are formed in region B and an array of metalcontact vias 624 are formed in region A. The semiconductor channels andmetal contact vias are formed between a pair of gate line slits 621 and622. Gate line slit 621 includes gate line slit 621A formed in region Aand gate line slit 621B formed in region B. Similarly, gate line slit622 includes gate line slit 622A and 622B formed in regions A and Brespectively. Gate line slits 621A, 621B, 622A, and 622B can each have arectangular shape as in the top view 601. Exemplary structure 600 alsoincludes other structures and/or features and are not shown in FIG. 6for simplicity and clarity.

To reduce gate electrode material agglomeration at the bottom of thevertical trenches, gate line slits in the wordline staircase region canhave greater widths than the array region. For example, gate line slits621B and 622B have width a and gate line slits 621A and 622A have widthb which can be greater than the width a. The increased width of gateline slit in the wordline staircase region can improve the etching rateat the bottom of the trench by providing chemical reactants or reactiveions of wet/dry etching processes easier access to the bottom of thetrench. Therefore, the wider opening can result in a wider opening atthe bottom of the vertical trenches, which in turn facilitates uniformgate electrode material dispose without metal agglomeration at thetrench bottoms. During the subsequent etch back process, the uniformgate electrode material dispose in the wordline staircase structures canlead to uniform etch back rate on the trench sidewalls and electricallyinsulate wordlines from different tiers.

The top view of exemplary structure 600 shown in FIG. 6 illustrates gateline slits 621A and 622A having rectangular openings. The width “b” ofgate line slits 621A and 622A measured in the y direction can bedifferent. For example, the width “b” can be greater than the width “a”by a nominal amount that is determined by various factors. For example,a minimal increase in width would likely result in minimal increase inthe width increase at the trench bottom, thus providing limitedbenefits. On the other hand, as the gate line slit is formed adjacent tothe semiconductor channels and metal contact vias, increasing the widthalso reduces the separation between the gate line slits and theiradjacent structures, which increases the risk of etching through theseparation and form undesirable electrical contact between the gate lineslits and adjacent structures. In addition, increasing the gate lineslit also occupies more device space and therefore has an impact ondevice density. The gate line slit design should consider and weigh atleast the above factors to provide nominal design for specific devices.In some embodiments, width b can be greater than width by an amount thatis between about 10 nm to about 50 nm. For example, width b can begreater than width a for about 20 nm. In some embodiments, gate lineslits 621A and 622A can have substantially the same width. In someembodiments, gate line slits 621A and 622A can have different widths,depending on the device needs and design. In some embodiments, dependingon the material composition of the dielectric material stack, width “a”may also be greater than width “b” to reduce metal agglomeration.

FIG. 7 illustrates exemplary structure 700 for forming thethree-dimensional memory device, according to some embodiments. FIG. 7is a top view 701 of exemplary structure 700 which includes wordlinestaircase region A and array region B. Regions A and B abut each otherat a region boundary 702, marked by the dotted line. Similar toexemplary structure 600 in FIG. 6, an array of semiconductor channels720 are formed in region B and an array of metal contact vias 724 areformed in region A. The semiconductor channels and metal contact viasare formed between a pair of gate line slits 721 and 722. Gate line slit721 includes gate line slit 721A formed in region A and gate line slit721B formed in region B. Similarly, gate line slit 722 includes gateline slit 722A and 722B formed in regions A and B respectively.Exemplary structure 700 also includes other structures and/or featuresand are not shown in FIG. 7 for simplicity and clarity

The top view of exemplary structure 700 shown in FIG. 7 illustrates gateline slits 721A and 722A having rectangular openings with a curved endextending in the x direction. Gate electrode material disposed at acorner of rectangular shaped slit (i.e., joints of sidewalls that areperpendicular to each other) is more challenging to achieve uniformdispose and etch back. Metal agglomeration can be formed in tight spaces(e.g., spaces formed in a corner between two sidewalls that are placedat 90° with each other) because dispose on both sidewalls accumulate insubstantially the same region and can cause metal agglomeration. Acurved end can reduce the agglomeration and further improves uniformdispose and etch back which in turn provides the benefit of effectivelyseparating adjacent wordline structures. In some embodiments, therespective curved ends 731 and 732 of gate line slits 721A and 722A canbe half circles connecting both sides (top and bottom sides shown inFIG. 7) of the gate line slits using width b as the diameter. In someembodiments, the curved ends can be any structure having curvaturedesigns or curved degrees suitable for the specific device needs anddesign goals. For example, the curved ends can include an arc-shapedstructure and the radius of the arc can be any suitable value. In someembodiments, curved ends 731 and 732 can have substantially the samecurvature design. In some embodiments, the curved ends can havedifferent curvature designs. Similar to the embodiments described abovein FIG. 6, depending on the material composition of the dielectricmaterial stack, width “a” may also be greater than width “b” to reducemetal agglomeration, in accordance with some embodiments.

FIG. 8 illustrates exemplary structure 800 for forming thethree-dimensional memory device, according to some embodiments. FIG. 8is a top view 801 of exemplary structure 800 which includes wordlinestaircase region A and array region B. Regions A and B abut each otherat a region boundary 802, marked by the dotted line. Similar toexemplary structures 600 and 700 in FIGS. 6 and 7 respectively, an arrayof semiconductor channels 820 are formed in region B and an array ofmetal contact vias 824 are formed in region A. The semiconductorchannels and metal contact vias are formed between a pair of gate lineslits 821 and 822. Gate line slit 821 includes gate line slit 821Aformed in region A and gate line slit 821B formed in region B.Similarly, gate line slit 822 includes gate line slit 822A and 822Bformed in regions A and B respectively. Exemplary structure 800 alsoincludes other structures and/or features and are not shown in FIG. 8for simplicity and clarity.

The top view of exemplary structure 800 shown in FIG. 8 illustrates gateline slits 821A and 822A having gradually increased openings with acurved end. The widths of the gate line slits increases as they extendin the x direction. As shown in FIG. 8, gate line slits 821A and 822Aabut gate line slits 821B and 822B respectively at the boundary betweenregions A and B, and can be in close proximity to semiconductor channels820. Therefore, gradually increasing the widths of gate line slits 821Aand 822A rather than having a uniform increased width can reduce therisk of impacting the semiconductor channels 820 by reducing thelikelihood of causing undesirable shorts or affecting the shapes ofsemiconductor channels 820. As shown above in FIGS. 4A-4D, as region Aextends in the positive x direction from the boundary between regions Aand B, the number of underlying wordline staircase structures decreasesand the depth of insulating material 413 gradually increases. Exemplarystructure 800 shown in FIG. 8 can be a portion of a three-dimensionalmemory device, and the three-dimensional memory device can includewordline staircase regions extending in other direction such as, forexample, negative y direction, positive and/or negative x direction,and/or any suitable directions. The gradually increased gate line slitopenings can be designed to adapt to the increasing depth of insulatingmaterial 413 to provide uniform dispose and etch back rate in the trenchalong the x direction which further prevents metal agglomeration.Similar to the curved end described above in FIG. 7, the curved end canreduce the agglomeration and further improves uniform dispose and etchback which in turn provides the benefit of effectively separatingadjacent wordline structures. In some embodiments, the respective curvedends 831 and 832 of gate line slits 821A and 822A can be similar to therespective curved ends 731 and 732 described above in FIG. 7. In someembodiments, curved ends 831 and 832 can have substantially the samecurvature design. The curved ends can include an arc-shaped structureand the radius of the arc can be any suitable value. In someembodiments, the curved ends can have different curvature designs. Insome embodiments, a horizontal distance “c” (measured in thex-direction) between the ends of gate line slits 821A and 822A (i.e.,portions of the gate line slits that are furthest away in the xdirection from the region boundary) and an end portion (a portion of themetal contact via that is furthest away from the region boundary in thex direction) of the last metal contact via (the metal contact via thatis furthest away from the region boundary in the x direction) is betweenabout 0.5 μm and about 2 μm. In some embodiments, the distance can beabout 1.5 μm. Similar to the embodiments described above in FIG. 6,depending on the material composition of the dielectric material stack,width “a” may also be greater than width “b” to reduce metalagglomeration, in accordance with some embodiments.

FIG. 9 is an illustration of an exemplary method 900 for formingthree-dimensional memory device, according to some embodiments. Forexplanation purposes, the operations shown in method 900 are describedin context of FIGS. 2A-8. In various embodiments of the presentdisclosure, the operations of method 900 can be performed in a differentorder and/or vary.

In operation 902, a substrate can be provided. FIGS. 2A and 2Billustrate an exemplary substrate in this operation. The substrate caninclude a base substrate and a material layer over the substrate. Thebase substrate can include any suitable material for forming thethree-dimensional memory structure. For example, the base substrate caninclude silicon, silicon germanium, silicon carbide, silicon oninsulator (SOI), germanium on insulator (GOI), glass, gallium nitride,gallium arsenide, and/or other suitable III-V compound. In someembodiments, the material layer can include an alternating stack ofinsulating layers and sacrificial layers, arranged along a verticaldirection over base substrate. In some embodiments, the sacrificiallayers include silicon nitride and the insulating layers include siliconoxide.

In operation 904, an alternating dielectric material stack, having astaircase structure, can be formed from the substrate provided inoperation 902. Referring to FIGS. 2A-2B, a number of alternatinglystacked insulating layer/sacrificial layer pairs can be formed in thestack. Referring to FIGS. 3A-3B, a staircase structure can be formed onthe alternating dielectric material stack. Further, as shown in FIGS. 4Aand 4B, a plurality of semiconductor channels can be formed through thestack and substantially into the base substrate. The semiconductorchannels can each include at least a dielectric core, a semiconductorchannel film, and a memory film. The semiconductor channels can beformed by sequentially depositing the memory film, the semiconductorchannel film, and the dielectric core using suitable methods.

In operation 906, gate line slits can be formed through the stack byopening trenches and removing the sacrificial layers, followed bydepositing and etching back the gate electrode material. Further,referring to FIGS. 4A-4B gate line slits through the stack can be formedfrom vertical trenches along the horizontal direction to divide thestack into a plurality of fingers. At least one of the gate line slitsinclude one or more openings along the horizontal direction to connectthe sacrificial layer/insulating layer pairs of adjacent fingers of thesame tier. The vertical trenches can be formed by patterning a mask overthe stack and etching the portions of the stack exposed by the mask. Arecess etch and/or a CMP process can be used to planarize the topsurface of the stack after the dielectric material is disposed. Metalcontact vias can be formed on the wordlines. One or more metal contactvias can be formed on the connected wordlines to conductively connectthe connected wordlines with an external circuit.

Further, referring to FIGS. 6-8, etching processes in the dielectricstack structure can form gate line slits having different widths alongthe x direction. In some embodiments, the widths of gate line slits inthe wordline staircase region is greater than widths of gate line slitsin the array region. The increased width of gate line slit in thewordline staircase region can be determined by the material compositionsin the dielectric stack structure, and can be designed to improve theetching rate at the bottom of the trench by providing chemical reactantsor reactive ions of wet/dry etching processes easier access to thebottom of the trench. Therefore, the wider opening can result in a wideropening at the bottom of the vertical trenches, which in turnfacilitates uniform gate electrode material dispose without metalagglomeration at the trench bottoms. During the subsequent etch backprocess, the uniform gate electrode material dispose in the wordlinestaircase structures can lead to uniform etch back rate on the trenchsidewalls and electrically insulate wordlines from different tiers. Thewidth can be determined by weighing a number of factors such as, forexample, the material composition in the wordline staircase region andarray regions, the risk of an increased gate line slit width affectingthe semiconductor channels, and the impact on device density due to thespace needed for an increased gate line slit width.

Referring to FIG. 6, gate line slits in the wordline staircase regioncan have rectangular openings where the width measured in the ydirection can be greater than the width of gate line slits in the arrayregions. In some embodiments, gate line slit width in the wordlinestaircase region can be greater than its width in the array region by anamount that is between about 10 nm to about 50 nm. For example, thewidth difference can about 20 nm. In some embodiments, the gate lineslits in the wordline staircase regions can have substantially the samewidth. In some embodiments, gate line slits in the wordline staircaseregions can have different widths, depending on the device needs anddesign.

Referring to FIG. 7, gate line slits can have rectangular openings witha curved end. A curved end can reduce the agglomeration at the bottom ofthe gate line slits and further improves uniform dispose and etch backwhich in turn provides the benefit of effectively separating adjacentwordline structures. In some embodiments, the curved ends of the gateline slits can be half circles connecting both top and bottom sides ofthe gate line slits (as viewed from the top) using gate line slit widthas the diameter. In some embodiments, the curved ends can be anystructure having curvature designs or curved degrees suitable for thespecific device needs and design. In some embodiments, curved ends ofgate line slits formed in the wordline staircase region can havesubstantially the same curvature design. In some embodiments, the curvedends can have different curvature designs.

Referring to FIG. 8, gate line slits in the wordline staircase regioncan have gradually increased openings with a curved end. The widths ofthe gate line slits increases as they extend in the x direction. Thegradually increased widths of gate line slits can reduce the risk ofimpacting the semiconductor channels by reducing the likelihood ofcausing undesirable shorts or affecting the shapes of semiconductorchannels. In addition, the gradually increased gate line slit openingscan be designed to adapt to the increasing depth of insulating materialformed in the wordline staircase region and provide uniform dispose andetch back rate in the trench along the x direction, which furtherprevents metal agglomeration. Further, the curved end at the end of gateline slits in the wordline staircase region can reduce the agglomerationand further improves uniform dispose and etch back which in turnprovides the benefit of effectively separating adjacent wordlinestructures. In some embodiments, the curved ends of gate line slits inthe wordline staircase structure can have substantially similar designs.In some embodiments, the curved ends can have different curvaturedesigns. In some embodiments, a horizontal distance between the ends ofgate line slits (a point on the curved end that is furthest away fromthe region boundary) and the last metal contact via (i.e., furthest awayfrom the region boundary) is between about 0.5 μm and about 2 μm. Insome embodiments, the distance can be about 1.5 μm.

The present disclosure describes a three-dimensional NAND memory devicein which gate line slits can have a greater width in the wordlinestaircase region compared to the widths in the array region. Increasingthe gate line slit width at the top surface of the wordline staircaseregion can lead to an increased width at the bottom of the gate lineslit. A benefit, among others, of increasing the gate line slit width inthe wordline staircase region is facilitating uniform metal depositionand avoid metal agglomeration at the bottom of the gate line slit.Uniform metal deposition within the gate line slit in turn providesuniform gate electrode material etch back and prevents current leakageor shorts between adjacent gate electrodes.

In some embodiments, a memory device includes a substrate and aplurality of wordlines extending along a first direction over thesubstrate. The first direction is along the x direction. The pluralityof wordlines form a staircase structure in a first region. A pluralityof channels are formed in a second region and through the plurality ofwordlines. The second region abuts the first region at a regionboundary. The memory device further includes a plurality of contactstructures formed in the second region. Each one contact structure ofthe plurality of contact structures is electrically connected to atleast one wordline of the plurality of wordlines. The memory device alsoincludes an insulating slit formed in the first and second regions andalong the first direction. A first width of the insulating slit in thefirst region measured in a second direction is greater than a secondwidth of the insulating slit in the second region measured in the seconddirection.

In some embodiments, a memory device includes a wordline staircaseregion extending along a first direction. The memory device alsoincludes an array region. The memory device further includes a pluralityof channels formed between adjacent slit structures of the plurality ofslit structures. The memory device also includes a plurality of slitstructures where each slit structure includes first and second slitstructures formed in the wordline staircase region and the array regionrespectively. The widths of the first and second slit structures aredifferent.

In some embodiments, a semiconductor device includes a substrate and aslit formed in the substrate. The slit includes a wordline staircaseslit abutting an array slit. The wordline staircase slit and array slitare respectively formed in wordline staircase and array regions. A widthof the wordline staircase slit is greater than a width of the arrayslit.

The foregoing description of the specific embodiments will so fullyreveal the general nature of the present disclosure that others can, byapplying knowledge within the skill of the art, readily modify and/oradapt for various applications such specific embodiments, without undueexperimentation, without departing from the general concept of thepresent disclosure. Therefore, such adaptations and modifications areintended to be within the meaning and range of equivalents of thedisclosed embodiments, based on the teaching and guidance presentedherein. It is to be understood that the phraseology or terminologyherein is for the purpose of description and not of limitation, suchthat the terminology or phraseology of the present specification is tobe interpreted by the skilled artisan in light of the teachings andguidance.

Embodiments of the present disclosure have been described above with theaid of functional building blocks illustrating the implementation ofspecified functions and relationships thereof. The boundaries of thesefunctional building blocks have been arbitrarily defined herein for theconvenience of the description. Alternate boundaries can be defined solong as the specified functions and relationships thereof areappropriately performed.

The Summary and Abstract sections may set forth one or more but not allexemplary embodiments of the present disclosure as contemplated by theinventor(s), and thus, are not intended to limit the present disclosureand the appended claims in any way.

The breadth and scope of the present disclosure should not be limited byany of the above-described exemplary embodiments, but should be definedonly in accordance with the following claims and their equivalents.

What is claimed is:
 1. A memory device comprising: a substrate; aplurality of wordlines extending along a first direction over thesubstrate, wherein the plurality of wordlines form a staircase structurein a first region; a plurality of channels formed in a second region andthrough the plurality of wordlines, wherein the second region abuts thefirst region at a region boundary; and an insulating slit formed in thefirst and second regions and along the first direction, wherein: theinsulating slit completely passes through the first and second regionsand along the first direction; a first width of the insulating slit inthe first region measured in a second direction is greater than a secondwidth of the insulating slit in the second region measured in the seconddirection; and the first width increases gradually beginning at theregion boundary and ending at an end structure of the insulating slit.2. The memory device of claim 1, wherein the first direction is parallelto a top surface of the substrate.
 3. The memory device of claim 1,wherein the second direction is horizontal and perpendicular to thefirst direction.
 4. The memory device of claim 1, wherein the firstwidth is greater than the second width by about 10 nm to about 50 nm. 5.The memory device of claim 1, wherein the second width is uniform alongthe first direction within the second region.
 6. The memory device ofclaim 1, wherein the end structure comprises a curved end structure. 7.The memory device of claim 6, wherein the curved end structure comprisesan arc-shaped structure.
 8. The memory device of claim 6, furthercomprising a plurality of contact structures formed in the first region,wherein each contact structure of the plurality of contact structures iselectrically connected to at least one wordline of the plurality ofwordlines, and respective portions of a contact structure of theplurality of contact structures and the curved end structure that arefurthest away from the region boundary are separated in the firstdirection by about 0.5 μm to about 2 μm.
 9. A memory device comprising:a wordline staircase region extending along a first direction; an arrayregion abutting the wordline staircase region at a region boundary; anda plurality of slit structures completely passing through the wordlinestaircase region and the array region, wherein each slit structurecomprises first and second portions formed in the wordline staircaseregion and the array region respectively, and a width of the firstportion gradually increases beginning at the region boundary and alongthe first direction.
 10. The memory device of claim 9, wherein theplurality of slit structures extend along the first direction and thewidth of the first portion is measured in a second direction that ishorizontal and perpendicular to the first direction.
 11. The memorydevice of claim 9, wherein the width of the first portion is greaterthan a width of the second portion by about 10 nm to about 50 nm. 12.The memory device of claim 9, wherein the width of the first portiongradually increases between the region boundary and an end structure ofthe first portion.
 13. The memory device of claim 9, wherein a slitstructure of the plurality of slit structures comprises a curved endstructure.
 14. The memory device of claim 13, wherein the curved endstructure comprises an arc-shaped structure.
 15. The memory device ofclaim 9, wherein the width of the first portion is greater than a widthof the second portion.
 16. A memory device comprising: first and secondwordlines in a wordline staircase region, wherein the first and secondwordlines extend along a first direction; an array region abutting thewordline staircase region at a region boundary; and a slit structurealong the first direction and completely passing through the wordlinestaircase region and the array region, comprising: a first portioncomprising a first width formed in the wordline staircase region betweenthe first and second wordlines, wherein the first width graduallyincreases beginning at the region boundary and along the firstdirection; and a second portion comprising a second width formed in thearray region, and the first and second widths are different.
 17. Thememory device of claim 16, wherein the slit structure continuouslyextends along the first direction and the first and second widths aremeasured in a second direction perpendicular to the first direction. 18.The memory device of claim 16, wherein the first width of the firstportion is greater than the second width of the second portion by about10 nm to about 50 nm.
 19. The memory device of claim 16, wherein thesecond width of the second portion is uniform along the first direction.20. The memory device of claim 16, wherein the end structure of firstportion comprises a curved end structure.